1. Field of the Invention
The present invention is related to a duplex printing apparatus for printing on both the front surfaces and the rear surfaces of sheets. In particular, the present invention is related to a duplex printing apparatus which is capable of securing time for ink which has been printed on the front surface to dry.
2. Description of the Related Art
Recently, there is desire to reduce the amount of paper sheets which are utilized, from the viewpoint of environmental problems. For this reason, duplex printing, in which printing is performed on both the front surfaces and the rear surfaces of sheets, is commonly being performed. Duplex screen printing apparatuses that perform screen printing on both surfaces of sheets have been proposed. An example of such a duplex screen printing apparatus is equipped with a first cylindrical drum and a second cylindrical drum. Screen printing stencils are wound about the outer peripheral surfaces of the first and second drums. The first drum performs printing onto the front surfaces of sheets, the sheets, of which the front surfaces have been printed on, are conveyed to the second drum, and the second drum performs printing onto the rear surfaces of the sheets.
In the duplex printing apparatus as described above, printing is performed onto the rear surfaces of sheet, the front surfaces of which have already been printed on. Therefore, there is a possibility that the sheets will become stained due to the ink on the front surfaces not being sufficiently dry during conveyance to the second drum and during printing onto the rear surfaces thereof.
Therefore, a duplex printing apparatus that performs printing such that sheets, of which the front surfaces have been printed on, are temporarily held for a predetermined amount of time on a stage to dry the ink on the stage, has been proposed in Japanese Unexamined Patent Publication No. 2005-029375.
However, the duplex printing apparatus disclosed in Japanese Unexamined Patent Publication No. 2005-029375 stacks sheets, of which the ink on the surfaces thereof are not dry, on the stage. Therefore, there is a possibility that rubbing of the printed surfaces and seepage of ink will cause the sheets to be stained. In addition, sheets, onto which large amounts of ink have been transferred, have high liquid content therein. Therefore, the close contact properties among the surfaces of the sheets will increase, and multiple sheets may be conveyed when attempting to convey the sheets one by one. In addition, the sheets may become corrugated due to absorption of liquid, which will result in unsuccessful conveyance.